The present invention relates to a new and improved method of fault location on a line in which at least one signal relating to a travelling wave is formed from the voltage and current at a test or measurement location. The invention further relates to an arrangement or apparatus for carrying out such method.
By "fault location" as used in the present connection there is to be understood the determination of the direction and/or distance of a line fault in relation to a test or measuring location with measuring arrangements for inspecting the line voltages and line currents.
In practice it is usually a matter of locating voltage-reducing faults on the line, i.e. short-circuits with small and often negligible residual voltage at the fault location.
The problem is usually solved with the help of electromechanical or electronic distance relays, which essentially compare the input impedance of the faulty line with that in a normal condition and accordingly assumes the presence or the formation of at least approximately sinusoidal input signals. Such test signals are however available after decay of the transient processes initiated by the occurrence of the fault. An appropriate delay time must therefore be brought into play. Even the connection in series of filters, which filter out a suitable frequency component from the initially present broad spectrum of the transient processes or events, likewise again gives rise to a delay through its impedance-loaded transient response, and in addition represents an unwanted, additional circuit cost.
It is generally sought to keep as small as possible the time interval from fault occurrence or fault detection and energization of the distance relays until the availability of reliable information about the fault direction or fault distance.
There is therefore desired a fault location method capable of functioning even during the transient events, with its actual course of operation coming into action with as little delay as possible.
In this connection fault location methods operating with travelling waves are already known. Here a specially generated test signal with steep wave-front is generated and caused to travel along the line to be supervised. The reappearance of the wave reflected at the discontinuity position of the fault to the transmitting or test location and the duration of the time interval necessary for go and return, in combination with the known wave velocity of the line provide the distance between fault and test locations.
Besides the requirement for a special transmitter, there is here present the disadvantage of sensitivity with respect to interfering signals, such as appear in particular on heavy current and especially in high-voltage lines with high intensity and in part with steep flanks. This sensitivity is due to the fact that in the final analysis it is a matter of signal flank detection, which amounts to time differential test methods. In addition the measurement is critical for fault location positions very near the test location because of the very small transit time.
There is further known from U.S. Pat. No. 3,590,368 an arrangement operating with travelling wave signals for localizing a fault location with reference to two test stations on a line. In the two test stations there are formed from the measured voltages and measured currents travelling wave signals appropriate to only a single direction of propagation and after multiplication of one of the signals with the complex transmission factor on the line section between the two test stations are compared with one another over a control line additional to the line to be supervised. Correspondence of the compared signals denoted freedom from faults, deviation denotes the presence of a fault in the line section between the test stations.